Various catalysts have been used to alkylate phenols with olefins. Traditionally, such alkylation reactions are carried out at atmospheric pressure with the reactants and catalyst in the liquid phase, referred to as "homogeneous catalysis", utilizing catalysts such as sulfuric acid, boron trifluoride, and aluminum chloride. Alkylation of phenols with olefins of up to 500,000 number average molecular weight have been disclosed, such as in U.S. Pat. No. 4,735,582, and EP Publication 440,507 A2. The drawback of homogeneous catalysis, of course, is the difficulty and expense in removing the catalyst from the liquid product.
In the attempt to find suitable solid (i.e. "heterogeneous") catalysts as an alternative to the traditional catalysts mentioned above, there have been proposed the use of more advanced catalysts in the last decade or so.
Zeolites have been described as useful in the alkylation of aromatics as described in U.S. Pat. Nos. 4,283,573; 4,731,497 and 4,954,663. The major drawback of zeolite catalysts, however, is that their catalytic activity is internal to their crystal structure. Hence, they are only effective upon reactants small enough to penetrate the pores of the zeolite crystal structure. Such catalysts are generally inefficient for any alkylating agent having more than 20 carbon atoms.
Mole sieves and exchange resins such as described in U.S. Pat. Nos. 4,323,714 and 4,849,569 and EP Publication 387,080 suffer similar problems to those of the aforementioned zeolites in that they are dependent upon the ability of the reactants to penetrate the resin structure. In general, these resins are less desirable than zeolites inasmuch as the relevant art teaches the use of alkylating agents of no more than 10 carbons in length. Amberlyst 15 has been utilized with success on alkylating agents having number average molecular weights in the thousands, but only at moderate rates of conversion.
Clays, layered materials and composites thereof are known such as described in UK Patent Application 2,120,953 and EP Application 400,857, but show no advantage over other catalysts insofar as the maximum size of the alkylation agent is concerned.
Directly relevant to the instant invention is U.S. Pat. No. 4,912,264 issued Mar. 27, 1990 to Sumitomo Chemical wherein alkylating agents comprising olefins having up to 13 carbon atoms are reacted with hydroxy-containing aromatics in the presence of a hydrated heteropoly acid and excess water. This patent indicates no or diminished yields for alkylating agents having more than 13 carbon atoms. Significantly, this method produces greater percentages of disubstituted product than monosubstituted. It is claimed that excess water is an advantage.
Also relevant is U.S. Pat. No. 3,346,657 issued Oct. 10, 1967, assigned to Gulf which refers to supporting a tungsten-based heteropoly acid upon a silica gel. High yields are obtained for dodecene-1 alkylation of benzene after calcination of the supported gel. The silica support is disclosed to be a major improvement over alumina supports.
Other disclosures of low molecular weight alkylations of aromatics in the presence of heteropoly catalysts are found in the scientific literature, such as T. Nishimura, T. Okuhara, and M. Misono, Chemistry Letters, p.1695 (1992) (alkylation of trimethyl benzene with cyclohexene and alkylation of phenol with 1-dodecene); R. Sebulsky and A.M. Henke, Industrial and Engineering Chemistry. Process Design and Development, Vol. 10, No. 2 (1971) (alkylation of benzene with 1-dodecene); and Reaction Kinetics and Catalysis Letters, Vol. 46, No. 1, p.17 (1992) (alkylation of p-tert--butyl phenol with hexene-1).
It is well known by those skilled in the art that as the molecular weight of the olefin used in an aromatic alkylation increases into the polymeric range, the alkylation becomes more difficult. Steric hindrance of the olefinic moiety and mass transfer limitations are recognized culprits. Increased acid strength improves yield, but is not always effective.